1. Field of the Invention
The present invention relates generally to earth boring rock bits and, more particularly, to rock bits in which the cone-type cutters are axially secured to the journal pins by means other than ball bearings.
2. Description of the Prior Art
A rotary rock bit usually comprises a plurality of legs welded together to form a bit body having one end threaded for attachment to a drill string. The lower end of each leg extends downwardly from the bit body and includes a journal pin extending radially inwardly for rotatively supporting a cone type cutter. Each cutter is adapted to roll along the bottom of the bore and is adapted to contact and disintigrate the earth formation at the bore bottom.
Present day rock bits usually include ball bearings located between the journal pin and the cutter to provide some thrust bearing support and to retain the cone on the journal pin. However, these ball bearings are not capable of absorbing axial thrust loads in either axial direction of the journal pin. Therefore, their main utility is for retention only. Other problems with utilizing ball bearings is that during operation the cone has an undesirable rocking movement and an in and out-thrust movement.
Alternatives to the ball bearings have been utilized in retaining the cutter onto the journal pin. One alternative is the utilization of an annular thrust member which is retained on the journal pin and secured to the cutter. Such thrust members are shown in U.S. Pat. Nos. 959,540, 979,496, 1,010,144, 1,010,407, 1,119,163, 1,124,241, 1,484,995, 1,692,793, 1,720,401 and 3,971,600. The shortcoming with these devices is that the annular thrust members have to be threadedly secured to the cutter. Such threaded connections are not desirable because of the hostile environment the cutters are subject to. These threads create high stress areas due to the sharp corners forming the threads thereby making the whole area susceptible to cracking and breaking. Moreover, special machines and tools are required to manufacture threads and to threadedly tighten the annular thrust members during assembly. The use of such tools is akward and positive tightening of the various members is not always guaranteed. Also, threaded details tend to loosen when the rock bit is in use.